The invention concerns a method for producing connecting ends on a hose piece having several metal layers, in particular, a strip wound metal hose piece, by fixing the overlapping metal layers of a hose having a larger length or of an endless hose in the region of the point of separation through welding to subsequently separate the hose piece from the longer hose or the endless hose. The invention also concerns a hose piece, in particular, a strip wound metal hose piece which comprises several metal layers and at least one connecting end in the region of which at least regions of the overlapping metal layers are welded together.
Hoses of this type comprising overlapping metal layers are used, in particular in the form of annular or helically strip wound hoses, as conduit elements in exhaust pipes of automotive vehicles. Due to their above-mentioned construction, they can accommodate certain length variations, as well as the bending and twisting which usually occur during operation of automotive vehicles, e.g. due to thermal expansion or vibration.
These conduit elements are manufactured, in particular, through helical winding of one or more layers of a metal strip. The positive connection of the neighboring regions of the strip or layers is effected through U-shaped profiles or folds. The production lines for such hoses are either endless or produce at least hose sections having a length of several meters.
For further processing, the strip wound hoses must be cut to a desired length. This separating process may not be effected by merely cutting perpendicularly to the hose axis, since fixation of neighboring layers would be partially destroyed and the strip end would burst open due to its internal tension leading to sharp tips or triangular protrusions at the strip end. Should a hose piece have such burst-open connecting ends, it cannot be further processed and must be rejected. Later fixing of the burst-opened metal layers in the region of the burst-open connecting ends is, in particular, not possible in practice, since the metal layers are exposed to bending loads.
In order to fix the connecting ends before separating off a hose piece from the longer hose or from an endless hose, the metal layers of the hose are conventionally fixed only mechanically in the region of the connecting ends (EP 1 281 904 A2). This may be effected through pressing, embossing, imprinting etc., of at least regions thereof. This requires, however, relatively expensive tools which must also be adapted to the respective hose geometry. Moreover, permanent fixing of the metal layers which would allow, in particular, later widening of the hose piece in the region of the connecting ends as is required for adjustment to the pipe diameter of neighboring pipe elements, is not possible in practice.
DE 44 11 246 A1 and EP 0 674 964 A1 describe a method for producing connecting ends on metal hoses of the above-mentioned type by laser welding a large number of welding points in the form of a stitch seam to fix the metal layers of an endless hose in the region of the subsequently produced connecting ends. Subsequent separation of the hose piece is effected by laser beam cutting.
One disadvantage is the substantial splashing during the required point welding of very oily and coated metal strips which can soil the processing optics and gas conduits. Moreover, two neighboring approximately parallel stitch seams or, at considerably reduced speed, one stitched seam must be produced, having a relatively large welding point diameter. This process is time consuming and therefore expensive. If the welding points have similar separations, there is always the fundamental risk that small residual triangular protrusions or nubs are formed after subsequent cutting off of the hose piece. The welded stitch seam at the terminating end of the strip wound hose tends to tear during a subsequent widening or calibration process leading to incomplete fixation in the region of the connecting ends. This can produce rejects, or at least considerably aggravate handling of such a hose piece. Subsequent widening or calibrating processes often produce breaks at the welded stitch seams in the longitudinal direction of the hose piece, which may extend over one or even more windings of the metal layers of the hose.
DE 198 51 173 C1 discloses a further method and a device for producing connecting ends on metal hoses of the above-mentioned type. The metal layers of the hose are also fixed by laser welding before the separating process, wherein a laser beam is guided continuously over the entire periphery of the hose piece thereby superposing a cyclic motion which subtends a finite angle with respect to the peripheral direction of the hose piece to produce the welding seam and generate an approximately sinusoidal or saw-tooth-shaped welding seam. This permits more effective and faster fixing of the metal layers in the region of the connecting ends of the hose piece and effectively prevents extensive splashing which occurs, in particular, during point welding. It however, also bears the danger that one or more metal layers are torn in the region of the connecting ends, in particular, during later widening or calibration processes of a hose piece produced in this manner.
It is therefore the underlying purpose of the invention to provide a simple and inexpensive method of the above-mentioned type which eliminates the described disadvantages and permits, in particular, perfect and load-resistant connection of the metal layers of the produced hose piece in the region of the connecting ends. The invention also concerns a hose piece produced in this manner.